hally

Hi Rennlisters,

my engine has developed a bit of an attitude problem recently.
It starts and idles / or drives for about 5mins then just cuts out cleanly.
It then has trouble restarting unless I let it sit for a while.

Watching the air/fuel gauge I could see it switch from open loop to closed loop after warming up and it ran for a while in closed loop (eg tested it sitting in neutral in the garage at 2000rpm for 6mins) before dying.

After trying to restart it a few times with partial success, there is black fuel smoke at the exhaust. Yet the way it cuts out cleanly makes me think a lack of fuel is the issue. I replaced the blue/black vacuum valve recently as the old one had snapped causing a vacuum leak, maybe a bit of plastic off this got sucked into the FPR or something.. Possibly the fuel smoke was due to flooding it a little attempting to restart a few times..

Do people think this sounds like a fuel or electrical issue.
Could a failing o2 sensor cause this?
Was thinking of disconnecting o2 sensor to see if that isolates the problem.

Thanks for any tips.

facboy

cap/rotor? that's what it was on my car.

speed/ref sensors?

Danno

Sounds like a fuel-problem.... perhaps the fuel-pump section of the DME relay?

Black smoke out the exhaust would be too rich, perhaps your FPR or fuel-dampener has failed?

hally

thanks fac & danno - I'll try my old 2.5 FPR as an experiment, should be a bit lean but OK for an idling test I imagine.
what about the dampner how would you validate this is working.
my distributor cap was replaced last year, but I guess you never know, can I test this somehow, or any visual inspection tell tale signs?
thanks again

facboy

on mine it was the rotor, not the cap. i dunno, on mine it was stumbling and dying etc. but if i got it up to high rpm it worked ok for some reason.

speed/ref sensors - i got told to try the water trick. next time it dies, pour water over the speed/ref sensors (they're at the back of the block), and see if it fires up right away. apparently they stop working when they get hot when they're on their way out, and the water cools them down quickly (or shorts out the open-circuit, or something).

hally

my RPM gauge is working fine, is this driven by same ref sensor that you are refering to?

facboy

i don't know...my guess is not. it's the crank-angle sensor, i don't think that would be used to calculate rpm, would it? i'm not much of an expert, it was a suggestion i was given by my mechanic when mine was going south.

hally

DME relay - check
Fuel pump - check
Fuel pressure - check
reference sensor - Bingo!

facboy

cool...well that's a pretty easy fix, isn't it? whee, i knew something for once.

hally

Clarks garage have a good page on speed and reference sensor replacement.http://www.clarks-garage.com/shop-manual/ign-02.htm

washington951

hally - how did you narrow this down? did you pull them and measure resistance values? wondering as i have had this hard cut-off situation, but its not repeated itself after one bad day. thanks.

hally

hi Brian,
sounds similiar to my problem (hard cutoff). it was intermittent / occasional for me also, then after a week degraded to consistent failure after a few minutes.
once i had checked out the fuel side of things and checked the price of those sensors I confess to handing it over to mechanic. waz looking expensive to play trial and error. they did a full DME test.
good luck with it.